Discovery of MK-5172, a macrocyclic hepatitis C virus NS3/4a protease inhibitor

Article abstract of DOI:10.1021/ml300017p

A new class of HCV NS3/4a protease inhibitors containing a P2 to P4 macrocyclic constraint was designed using a molecular modeling-derived strategy. Building on the profile of previous clinical compounds and exploring the P2 and linker regions of the series allowed for optimization of broad genotype and mutant enzyme potency, cellular activity, and rat liver exposure following oral dosing. These studies led to the identification of clinical candidate 15 (MK-5172), which is active against genotype 1-3 NS3/4a and clinically relevant mutant enzymes and has good plasma exposure and excellent liver exposure in multiple species.

Full text of DOI:10.1021/ml300017p

Letter
pubs.acs.org/acsmedchemlett
Discovery of MK-5172, a Macrocyclic Hepatitis C Virus NS3/4a
Protease Inhibitor
Steven Harper,*,⊥ John A. McCauley,*,† Michael T. Rudd,† Marco Ferrara,⊥ Marcello DiFilippo,⊥
Benedetta Crescenzi,⊥ Uwe Koch,∇ Alessia Petrocchi,⊥ M. Katharine Holloway,∥ John W. Butcher,†
Joseph J. Romano,† Kimberly J. Bush,† Kevin F. Gilbert,† Charles J. McIntyre,† Kevin T. Nguyen,†
Emanuela Nizi,⊥ Steven S. Carroll,‡ Steven W. Ludmerer,‡ Christine Burlein,‡ Jillian M. DiMuzio,‡
Donald J. Graham,‡ Carolyn M. McHale,‡ Mark W. Stahlhut,‡ David B. Olsen,‡ Edith Monteagudo,#
Simona Cianetti,# Claudio Giuliano,# Vincenzo Pucci,# Nicole Trainor,§ Christine M. Fandozzi,§
Michael Rowley,⊥ Paul J. Coleman,† Joseph P. Vacca,† Vincenzo Summa,⊥ and Nigel J. Liverton†
†
‡
§
∥
Departments of Medicinal Chemistry, Antiviral Research, Drug Metabolism, and Chemistry, Modeling and Informatics,
Merck Research Laboratories, West Point, Pennsylvania 19486, United States
⊥
#
Departments of Medicinal Chemistry, Drug Metabolism, and ∇Molecular Modeling, IRBM, Merck Research Laboratories,
Rome, Italy
S
* Supporting Information
ABSTRACT: A new class of HCV NS3/4a protease inhibitors containing a P2 to P4
macrocyclic constraint was designed using a molecular modeling-derived strategy. Building
on the profile of previous clinical compounds and exploring the P2 and linker regions of
the series allowed for optimization of broad genotype and mutant enzyme potency, cellular
activity, and rat liver exposure following oral dosing. These studies led to the identification
of clinical candidate 15 (MK-5172), which is active against genotype 1−3 NS3/4a and
clinically relevant mutant enzymes and has good plasma exposure and excellent liver
exposure in multiple species.
KEYWORDS: hepatitis C, HCV, MK-5172, macrocycle, genotype 3a, mutant enzymes
epatitis C virus (HCV) is a chronic liver infection that
We have disclosed a molecular modeling-derived strategy
that led us to design HCV NS3/4a protease inhibitors that
contain the P2 to P4 macrocyclic constraint.12 This design
arose from an analysis of the crystal structure of full-length
NS3/4A with and without inhibitors docked in the active site.13
Our strategy coupled with a modular synthetic approach, which
relies on a key ring-closing metathesis (RCM) reaction,14
allowed for the rapid exploration of these molecules and the
identification of clinical candidates, vaniprevir (1)15,16 and
MK-1220 (2).17 Herein, we describe the discovery of a clinical
candidate with broad activity across genotypes (gt) and resis-
tant HCV variants.18,19
With the development of vaniprevir progressing, we set a
goal for the ongoing discovery program to be the identification
of a second generation NS3/4a protease inhibitor. We wanted
to maintain or improve the PK profile seen with our previous
compounds and make significant improvements in activity
against the gt 3a enzyme as well as key clinically relevant gt 1
H
affects an estimated 130−170 million people worldwide.1,2
HCV displays a high degree of genetic heterogeneity and can
be classified into six major genotypes with different geographic
distributions: genotypes 1, 2, and 3 account for more than 90%
of the infections in the developed world. Treatment for HCV is
based on combination therapy with pegylated interferon-α and
ribavirin.3 Sustained viral response is seen in ∼45% of HCV
genotype 1-infected patients treated for 48 weeks and in ∼80%
of genotype 2- and 3-infected patients treated for 24 weeks.
Interferon and ribavirin therapy is also associated with a num-
ber of serious side effects, limiting the number of patients who
may be treated.4
There is a compelling medical need for new oral therapeutic
agents with improved efficacy and tolerability. Several
promising antiviral targets for HCV have emerged,5 with
NS3/4a protease inhibitors showing perhaps the most dramatic
antiviral effects.6 Clinical proof of concept for this mechanism
was first achieved with BILN-2061.7 Other compounds have
entered clinical trials, including telaprevir8 and boceprevir,9
both of which are now marketed treatments for use in com-
bination with a standard of care. Compounds currently in deve-
lopment include TMC-43510 and ITMN-191.11
Received: January 19, 2012
Accepted: February 26, 2012
Published: March 2, 2012
© 2012 American Chemical Society
332
dx.doi.org/10.1021/ml300017p | ACS Med. Chem. Lett. 2012, 3, 332−336

ACS Medicinal Chemistry Letters
Letter
cyan. All three compounds adopt similar conformations as
expected, but it is clear that both compounds 4 and 5 extend
further into the S2 pocket of the active site than compound 3.
Furthermore, this pocket is a conserved region between gt 1
and gt 3a, leading us to hypothesize that increasing contacts
with the conserved regions of the active sites of the two
genotypes should lead to increases in activity at gt 3a without
causing a loss in potency versus gt 1. It is also clear from the
modeling that the P2 to P4 linker falls into a region of the
active site that is not conserved between genotypes and is also
the region where two important gt 3a polymorphisms occur.
The docked poses of 4 and 5 suggest that the addition of a
larger P2 substituent may also bias the macrocyclic ring to shift
toward these residues, possibly improving complementarity to
the gt 3a site, especially with respect to the R123T polymorph,
which presumably leads to a significantly different active site
surface in this region. In addition to the D168Q difference
between gt 1b and gt 3a, D168 and R155 mutations are
observed in the gt 1b enzyme in clinical studies, and these
mutations cause potency shifts against both vaniprevir and
MK-1220 (1 and 2, see Table 2). This second observation led
us to hypothesize that removing steric bulk from the P2 region
of the molecule as well as increasing the flexibility of our P2 to
P4 macrocylic linker may allow for further improvements in gt
3a activity and mutant profile.
To test these hypotheses, compound 6, a bicyclic analogue of
5, was targeted. This compound was designed by removing two
of the carbons of the tricylic system, effectively lengthening the
P2 to P4 linker by two carbons and maintaining the interaction
with the conserved pocket, which seems to enhance gt 3a
activity. Compound 6 maintained excellent gt 1 activity (Ki =
0.06 nM) and liver exposure (25 μM) and showed good gt 3a
(Ki = 130 nM) activity considering that a large structural
change had been made. This result with compound 6 led us to
reconsider results with some compounds made early in the
program. Compounds 7 and 8 have simple 2-pyridyl and 3-
pyridyl substituents in the P2 position and do not have the gt 1
potency seen in advanced NS3/4a inhibitors. However, when
just the relative potency of these compounds is considered,
compound 8 seems to have an advantage with regard to gt 3a
potency. Moving the nitrogen from the 2-pyridyl position (7)
to the 3-pyridyl position (8) leads to a 2-fold reduction in
potency vs gt 1b (Ki = 1.1 vs 1.9 nM) but also leads to a 2-fold
increase in potency against the gt 3a enzyme (Ki = 1200 vs
520 nM). On the basis of modeling, this result is difficult to
explain, as there does not seem to be a specific hydrogen-
bonding interaction associated with the pyridyl nitrogen in
either position. This led us to hypothesize a more favorable
Table 1. In Vitro Activity
a
Ki (nM)
1b replicon IC50
rat [liver] at 4 h
b
c
compd
1b
3a
50% NHS (nM)
(μM)
3
4
5
6
7
8
9
0.02
0.05
0.05
0.06
1.1
200
45
10
21
19
7.8
96
12
19
130
1200
520
26
21
25
ND
ND
44
ND
ND
0.6
1.9
0.08
a
NS3/4a protease time-resolved fluorescence assay, mean of n ≥ 3
b
c
measurements. Cell-based replicon assay, mean of n ≥ 3. Liver levels
from PK experiments described in the Supporting Information.
mutant enzymes. Looking back at the gt 3a enzyme potency in
previous series led us to the following observation: a consistent
trend for increasing gt 3a activity was observed with the addi-
tion of a large substituent to the P2 heterocycle. For example,
the gt 3a activity of compound 3 (Ki = 200 nM, Table 1) was
improved by approximately 4-fold with the addition of a phenyl
group to give closely related compound 4 (Ki = 45 nM). On the
basis of this observation, we undertook a systematic investi-
gation of substituents at this position of the P2 quinoline, which
will be published elsewhere. As part of this investigation, we
also made a small number of fused ring analogues exemplified
by tricylic compound 5, which exhibited greatly improved gt 3a
enzyme activity (Ki = 12 nM). This represented a 16-fold
increase in gt 3a potency over bicyclic compound 3 and showed
that a fused ring could give results similar to those seen with
quinoline substituents. This increase in potency was accom-
panied by an increase in rat liver exposure to 96 μM at the 4 h
time point versus 21 μM for compound 3.
Compounds 3−5 were docked in both the gt 1 and the gt 3a
NS3/4a active site via molecular modeling in an effort to
explain this observed increase in gt 3a activity. Figure 1 shows
the three compounds docked in the gt 1b active site, and the
major differences between the two genotypes are highlighted in
Figure 1. Compounds 3 (A), 4 (B), and 5 (C) docked in the gt 1b NS3/4a active site. Cyan = areas of diversity between the gt 1b and gt 3a
enzymes. White = conserved areas.
333
dx.doi.org/10.1021/ml300017p | ACS Med. Chem. Lett. 2012, 3, 332−336

ACS Medicinal Chemistry Letters
Letter
Table 2. In Vitro Activity
a
Ki (nM)
b
c
compd
1b
3a
54
70
2.8
1b R155K
1b A156T
1b A156V
1b D168V
1b replicon IC50 50% NHS (nM)
rat [liver] at 4 h (μM)
1
2
0.05
0.09
0.02
0.02
0.02
0.02
0.02
0.02
19
22
540
18
88
790
79
77
19
11
37
18
28
16
13
7.4
9.9
23
15
27
10
11
12
13
14
15
0.32
0.20
0.16
0.07
0.02
0.07
ND
ND
ND
0.06
0.05
1.5
63
4.0
27
80
1.9
12
64
9.8
6.3
20
0.39
0.31
0.70
2.4
2.9
5.3
11
5.7
12
0.14
23
a
b
c
NS3/4a protease time-resolved fluorescence assay, mean of n ≥ 3 measurements. Cell-based replicon assay, mean of n ≥ 3. Liver levels from PK
experiments described in the Supporting Information.
electrostatic interaction with R155 in the case of compound 8
or a change in hydrogen bonding to active site water molecules.
On the basis of the results with 7 and 8, we performed this
same nitrogen switch on bicyclic 2-quinoline 6, giving 3-
quinoline 9, which leads to a 5-fold increase in gt 3a potency
(Ki = 26 nM). Although liver exposure was markedly reduced
(4 h liver exposure: 9 = 0.6 μM vs 6 = 26 μM), compound 9
emerged as a key lead for the second generation program, and
the focus became improving liver exposure as well as evaluation
of potency vs gt 1b mutant enzymes observed in clinical studies
with vaniprevir.20
In general, increasing potency against the A156 mutants was
very difficult, because as seen in Figure 2, the P2−P4 macro-
We previously observed that increasing lipophilicity in the P2
to P4 macrocylic series can lead to increases in liver ex-
posure.15,17 Adding a dimethyl linker substituent to compound
9 gave 10 and led to only a slight increase in liver exposure
(Table 2). This compound, however, had an improved Ki of 2.8
nM against the gt 3a enzyme, representing an almost 20-fold
improvement over both of our previous clinical candidates, 1
(gt 3a Ki = 54 nM) and 2 (gt 3a Ki = 70 nM). Further profiling
of 10 showed that activity against the key R155K mutant (Ki =
0.32 nM) had been improved by almost 50-fold in comparison
to both 1 (gt 1b R155K Ki = 19 nM) and 2 (gt 1b R155K Ki =
15 nM). The activity of 10 vs the A156 mutants was improved
by 10−30-fold in relation to compound 2 but was comparable
to that of compound 1. Saturation of the linker olefin of 10
gave 11, which had a similar potency profile but showed a
40-fold increase in rat liver exposure to 63 μM after a 5 mg/kg
oral dose at 4 h. These dramatic changes in rat liver exposure
have been observed throughout the program and highlight the
need for a rat liver screening strategy that we have adopted.15,17
Substituent effects were studied on the quinoline scaffold, and a
7-methoxy substituent (12) was optimal for activity, giving
slight increases in potency against gt 3a and 1b mutants R155K,
A156T and A156V.
Figure 2. Comparison of the energy-minimized conformations of
compounds 12 (magenta) and 14 (green) docked in the gt 1b NS3/4a
active site.
cyles sit almost directly on top of this residue. The activity
against R155 and D168 mutants was somewhat more addre-
ssable because the P2 substituent in the quinoline series mostly
avoids this region of the active site. One observed change that
led to improvement in A156 activity was the installation of a
fused ring linker. This effect was seen in a variety of compound
subclasses throughout the program, and details will be publi-
shed elsewhere. In this case, fusion of a cyclopentyl ring gave
compound 13 and resulted in a broad activity profile against
genotypes and key mutant enzymes (Table 2). Adjusting to a
fused cyclopropyl further improved the activity and gave a
compound (14) with excellent liver exposure. Modeling results
with compounds 12 and 14 give some insight into the reasons
for the 4−10-fold improvement against A156 mutant enzymes
(Figure 2). The cyclopropyl constraint of 14 seems to shift the
macrocycle away from the A156 residue as compared to
334
dx.doi.org/10.1021/ml300017p | ACS Med. Chem. Lett. 2012, 3, 332−336

ACS Medicinal Chemistry Letters
Letter
a
compound 12. Because the A156 residue is positioned close to
the middle of the macrocyclic ring, this slight shift may allow
more space for the macrocycle of 14 to accommodate the
A156T or A156V mutation. Another potential explanation
could be that the constraint restricts bond rotation leading to a
decreased entropic penalty upon binding and gives an overall
increase in potency. Compound 14 met our potency and PK
criteria and was evaluated in a battery of studies as a prelude to
its selection as a development candidate.
Scheme 1. Synthesis of Compound 15 (MK-5172)
During this candidate workup, an important pharmacokinetics-
related issue regarding the behavior of pharmaceutical salts
of 14 emerged and represented a major development hurdle.
While the crystalline potassium salt of 14 has good aqueous
solubility (9.7 mg/mL), it readily disproportionates to a
crystalline zwitterionic form that has a greatly reduced aqueous
solubility of <0.009 mg/mL. This behavior is driven by the
moderate basicity of the quinoline P2 group of 14 (calculated
pKa = 4.47)21 along with moderate acidity of the
acylsulfonamide (calculated pKa = 3.67). In vivo, this process
is promoted in the stomach where the native pH of the dosing
solution is attenuated, giving rise to nonreproducible
pharmacokinetics.22 Poor absorption of the crystalline zwitter-
ionic form of 14 that is formed in vivo significantly capped the
achievable plasma and liver exposures of 14 in preclinical
species. Given the excellent overall profile of compound 14, we
examined alternative P2 heterocycles with less basic function-
ality that would potentially maintain a similar potency and PK
profile. From this work, P2 quinoxalines emerged as the most
promising subclass, with lower pKa reducing the risk of
zwitterion formation (calculated pKa ∼ 1.2). Incorporating a
quinoxaline into our framework gave compound 15. Overall,
compound 15 maintained the excellent potency against the gt
3a enzyme as well as a broad panel of mutant enzymes, has
excellent potency in the replicon system [gt 1b IC50 (50%
NHS) = 7.4 nM; gt 1a IC50 (40% NHS) = 7 nM], and showed
excellent rat liver exposure. The potassium salt of 15 showed
aqueous solubility of 1.8 mg/mL, somewhat lower than 14;
however, no disproportionation was observed, making this
compound a viable development candidate.
All of the P2−P4 macrocyclic compounds shown were
prepared using a generally similar synthetic sequence.15,17
Specifically for compound 15, the synthesis starts with 4-
methoxy-phenylenediamine hydrochloride, which was heated
with diethyloxalate to give 17 in 69% yield (Scheme 1).
Chemoselective chlorination with thionyl chloride followed
by addition to activated cis-hydroxyproline derivative 1823 and
deprotection then led to intermediate 19 in 69% yield.
Straightforward amide coupling with 20, prepared in enan-
tiopure form in six steps, led to chloroquinoxaline 21. Next,
while vinylation proceeded smoothly, the key RCM using the
Zhan 1b catalyst24 was problematic, and the desired macrocycle
was isolated in 25% yield. Reduction of the resulting olefin gave
macrocycle 22, which was readily converted to 15 (MK-5172)
in 89% yield by hydrolysis and coupling to the known
cyclopropylamino acylsulfonamide 23.25
a
Reagents and conditions: (a) Diethyloxalate, TEA, 150 °C. (b)
Thionyl chloride, DMF, 110 °C. (c) Compound 18,23 Cs2CO3,
NMP. (d) HCl, dioxane. (e) Compound 20, HATU, DIPEA, DMF.
(f) Potassium vinyltrifluoroborate, TEA, dichloro[1,1-bis-
(diphenylphosphino)ferrocene]palladium(II) chloride, EtOH. (g)
Zhan 1B catalyst,24 DCE. (h) H2, 10% Pd/C, MeOH, dioxane.
(i) LiOH, THF, water. (j) Compound 23,25 TBTU, DIPEA, DMAP,
DMF.
Table 3. Pharmacokinetic Parameters for the Potassium Salt
of 15
a
po
Vd
T1/2
AUC
[liver] 4 h
(μM)
[liver] 24 h
b
species Cl
(L/kg)
(h)
(μM h)
(μM)
rat
28
3.1
0.7
1.4
3.0
0.7
0.4
23
0.2
1.4
dog
5
ND
a
Rat iv (2 mg/kg, n = 3, DMSO), dog iv (0.5 mg/kg, n = 3, DMSO),
rat po (5 mg/kg, n = 3, PEG400), and dog po (1 mg/kg, n = 3,
PEG400). mL/min/kg.
b
which is >25-fold higher than the IC50 in the replicon assay
with 50% NHS.
When dosed to dogs, compound 15 shows low clearance of 5
mL/min/kg and a 3 h half-life after iv dosing and has good
plasma exposure (AUC = 0.4 μM h) after a 1 mg/kg oral dose.
Dog liver biopsy studies showed that the liver concentration of
15 after the 1 mg/kg oral dose is 1.4 μM at the 24 h time point.
Similar to its behavior in rats, 15 demonstrates effective par-
titioning into liver tissue and maintains high liver concentration,
relative to potency, 24 h after oral dosing in dogs.
In summary, initial screening for gt 3a activity along with
molecular modeling has led to the discovery of a series of P2
quinoline macrocycles with excellent broad activity vs NS3/4a
genoytpes and clinically observed gt 1b mutant enzymes. This
series was optimized for enzyme activity and liver exposure in
preclinical species. Compound 15 emerged from this series via
the introduction of a mildly basic quinoxaline P2 heterocycle to
deal with disproportionation issues with the more basic quino-
line P2 heterocycle. We believe the combination of good PK,
and broad enzyme potency gives compound 15 the potential
to be an important second generation NS3/4a protease inhibi-
tor that could be a cornerstone of an all-oral treatment for
hepatitis C. Further studies of 15 (MK-5172), including clinical
investigations of the pharmacokinetic and efficacy profile, are
ongoing.18
The pharmacokinetic properties of the potassium salt of
compound 15 were evaluated in multiple species (Table 3). In
rat, 15 showed a plasma clearance of 28 mL/min/kg and a
plasma half-life of 1.4 h. When dosed orally at 5 mg/kg, the
plasma exposure of 15 was good with an AUC of 0.7 μM h.
The liver exposure of the compound is quite good (23 μM
at 4 h), and 15 remains in liver 24 h after a single 5 mg/kg
oral dose. At 24 h, the liver concentration of 15 is 0.2 μM,
335
dx.doi.org/10.1021/ml300017p | ACS Med. Chem. Lett. 2012, 3, 332−336

ACS Medicinal Chemistry Letters
Letter
(16) Liverton, N. J.; Carroll, S. S.; DiMuzio, J. M.; et al. MK-7009: A
Potent and Selective Inhibitor of Hepatitis C Virus NS3/4a Protease.
Antimicrob. Agents Chemother. 2010, 54, 305−311.
(17) Rudd, M. T.; McCauley, J. A.; Butcher, J. W.; et al. Discovery of
MK-1220: A Macrocyclic Inhibitor of Hepatitis C Virus NS3/4a
Protease with Improved Preclinical Plasma Exposure. ACS Med. Chem.
Lett. 2011, 2, 207−212.
ASSOCIATED CONTENT
■
S
* Supporting Information
Assay and synthetic procedures and data for selected
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
(18) Summa, V.; Ludmerer, S. W.; McCauley, J. A.;et al. MK-5172, a
selective inhibitor of Hepatitis C Virus NS3/4a protease with broad
activity across genotypes and resistant variants. Antimicrob. Agents
Chemother. Submitted for publication.
(19) Harper, S.; Summa, V.; Liverton, N. J.; McCauley, J. A.
Macrocyclic Quinoxaline Compounds as HCV NS3 Protease
Inhibitors. U.S. Patent 7,973,040, 2011.
(20) Manns, M. P.; Gane, E. J.; Rodriguez-Torres, M.; et al. Sustained
viral response (SVR) rates in genotype 1 treatment-naive patients with
chronic Hepatitis C (CHC) infection treated with Vaniprevir (MK-
7009), a NS3/4A protease inhibitor, in combination with pegylated
Interferon alfa-2A and Ribavirin for 28 days. Hepatology 2010,
52 (4 Suppl.), 361A.
AUTHOR INFORMATION
■
Corresponding Author
*Tel: 215-652-4133. Fax: 215-652-3971. E-mail: john_mccauley@
merck.com; S.Harper@irbm.it.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Dr. Charles W. Ross, III, and Vince Van Nostrand for
determination of high-resolution mass spectra.
(21) MarvinSketch, publisher. ChemAxon Ltd., version 3.5.2; 2004;
http://www.chemaxon.com/products/marvin/marvinsketch.
(22) Monteagudo, E.; Fonsi, M.; Chu, X.; et al. The metabolism and
disposition of a potent inhibitor of hepatitis C virus NS3/4A protease.
Xenobiotica 2010, 40, 826−839.
(23) Arasappan, A.; Chen, K. X.; Njoroge, F. G.; et al. Novel
Dipeptide Macrocycles from 4-Oxo, -Thio, and -Amino-Substituted
Proline Derivatives. J. Org. Chem. 2002, 67, 3923−3926.
(24) CAS# 918870-76-5.
REFERENCES
■
(1) WHO. Hepatitis CGlobal prevalence (update). Wkly.
Epidemiol. Rec. 1999, 74, 425−427.
(2) Liang, T. J.; Heller, T. Pathogenesis of hepatitis C-associated
hepatocellular carcinoma. Gastroenterology 2004, 127, S62−S71.
(3) Hadziyannis, S. J.; Sette, H.; Morgan, T. R.; et al. Peginterferon-
alpha2a and ribavirin combination therapy in chronic hepatitis C: A
randomized study of treatment duration and ribavirin dose. Ann.
Intern. Med. 2004, 140, 346−355.
(25) Li, J.; Smith, D.; Wong, H. S.; et al. A Facile Synthesis of 1-
Substituted Cyclopropylsulfonamides. Synlett 2006, 725−728.
(4) Fried, M. W. Side effects of therapy of hepatitis C and their
management. Hepatology 2002, 36, S237−S244.
(5) Gordon, C. P.; Keller, P. A. Control of hepatitis C: A medicinal
chemistry perspective. J. Med. Chem. 2005, 48, 1−20.
(6) Chen, K. X.; Njoroge, F. G. A review of HCV protease inhibitors.
Curr. Opin. Invest. Drugs 2009, 10, 821−837.
(7) Lamarre, D.; Anderson, P. C.; Bailey, M.; et al. An NS3 protease
inhibitor with antiviral effects in humans infected with hepatitis C
virus. Nature 2003, 426, 186−189.
(8) Perni, R. B.; Almquist, S. J.; Byrn, R. A.; et al. Preclinical profile of
VX-950, a potent, selective, and orally bioavailable inhibitor of
hepatitis C virus NS3−4A serine protease. Antimicrob. Agents
Chemother. 2006, 50, 899−909.
(9) Malcolm, B. A.; Liu, R.; Lahser, F.; et al. SCH 503034, a
mechanism-based inhibitor of hepatitis C virus NS3 protease,
suppresses polyprotein maturation and enhances the antiviral activity
of alpha interferon in replicon cells. Antimicrob. Agents Chemother.
2006, 50, 1013−1020.
(10) Lin, T.-I.; Lenz, O.; Fanning, G.; et al. In Vitro Activity and
Preclinical Profile of TMC435350, a Potent Hepatitis C Virus Protease
Inhibitor. Antimicrob. Agents Chemother. 2009, 53, 1377−1385.
(11) Seiwert, S. D.; Andrews, S. W.; Jiang, Y.; et al. Preclinical
Characteristics of the Hepatitis C virus NS3/4A Protease inhibitor
ITMN-191 (R7227). Antimicrob. Agents Chemother. 2008, 52, 4432−
4441.
(12) Liverton, N. J.; Holloway, M. K.; McCauley, J. A.; et al.
Molecular modeling based approach to potent P2-P4 macrocyclic
inhibitors of hepatitis C NS3/4a protease. J. Am. Chem. Soc. 2008, 130,
4607−4609.
(13) Yao, N.; Reichert, P.; Taremi, S. S.; et al. Molecular views of
viral polyprotein processing revealed by the crystal structure of the
hepatitis C virus bifunctional protease-helicase. Structure 1999, 7,
1353−1363.
(14) Grubbs, R. H. Olefin metathesis catalysts for the preparation of
molecules and materials (Nobel Lecture). Angew. Chem., Int. Ed. 2006,
45, 3760−3765.
(15) McCauley, J. A.; McIntyre, C. J.; Rudd, M. T.; et al. Discovery of
Vaniprevir (MK-7009), a Macrocyclic Hepatitis C Virus NS3/4a
Protease Inhibitor. J. Med. Chem. 2010, 53, 2443−2463.
336
dx.doi.org/10.1021/ml300017p | ACS Med. Chem. Lett. 2012, 3, 332−336